Unchecked external calls detection

When this applies

• Low-level call, delegatecall, staticcall, send
• ERC-20 transfer / transferFrom / approve (non-SafeERC20)
• Calls to user-provided addresses
• Multi-call patterns that don't propagate failures
• Try-catch swallowing all errors

Detection patterns

Ignored .call return (HIGH)

(bool ok,) = target.call(data);   // ← ok unused
// or worse:
target.call(data);                 // ← Solidity ≥0.5 still allows this with warning

Always require(ok, "call failed"); unless an intentional best-effort.

ERC-20 without SafeERC20 (HIGH)

USDT and other non-conformant tokens don't return bool. Naive call:

IERC20(usdt).transfer(to, amt);   // ← reverts on USDT due to ABI mismatch

Use OZ SafeERC20's safeTransfer which handles missing return values.

Return-data check missing (HIGH)

Even compliant ERC20 returning false instead of reverting is silently passed:

bool ok = token.transfer(to, amt);   // ← ok unused, returns false on failure

try/catch swallows everything (MEDIUM-HIGH)

try external.call() { /* … */ }
catch { /* silently ignored */ }

Without inspecting catch (bytes memory reason), you lose all info; transitioning a critical revert into a silent success is a bug.

Address with no code (HIGH on call)

(bool ok,) = target.call(data);
require(ok);

ok = true even if target is an EOA with no contract — call returns true. Add target.code.length > 0 check.

Permit followed by transferFrom — permit silently revertable (MEDIUM)

If permit reverts (because it was already used), the consuming transferFrom continues with a stale allowance. Use try/catch only to skip the permit reuse case.

Multicall fail-skip (HIGH)

Some routers continue on per-call failure. If a treasury sweeps via multicall, a single failed call could drop revenue.

selfdestruct / transfer no longer guaranteed on L2s with reduced gas

Forwarding 2300 gas is brittle on Berachain/Arbitrum/etc. — see [[dos-vectors]].

Severity rubric

Remediation patterns

• Always check (bool ok, bytes memory ret) = target.call(...) and require(ok, ...).
• For ERC-20: use OZ SafeERC20 everywhere.
• After .call to dynamic addresses, check target.code.length > 0 before relying on return.
• Replace transfer / send with (bool ok,) = to.call{value: amt}("") + check.
• For best-effort hooks (event-style), document with a comment and consider returning a status code rather than silently succeeding.

False-positive notes

• A .call whose only side-effect-on-failure is a UX message can be best-effort — Info.
• Solady / Solmate sometimes use bare call with custom assembly checks — verify the surrounding bytes are inspected.

Related

• [[token-compatibility]] — non-conformant ERC20s
• [[dos-vectors]]
• [[reentrancy]]